Comment 89 for bug 1244090

Discovered that it is unrelated to gnome-settings-daemon, you can try the following script. It binds '1' key and pressing it causes the same behavior:

#!/usr/bin/python
import dbus
bus = dbus.SessionBus()
o = bus.get_object('org.gnome.Shell', '/org/gnome/Shell')
code = o.GrabAccelerator('1', 0, dbus_interface='org.gnome.Shell')
try:
  raw_input("Grab set to key '1', press Enter to continue and ungrab")
finally:
  print o.UngrabAccelerator(code, dbus_interface='org.gnome.Shell')

(at least in Ubuntu, someone with vanilla Gnome can try it too. Ubuntu uses compiz to implement org/gnome/Shell/GrabAccelerator.)